Steroid hormones are small regulatory molecules that profoundly influence basic processes of growth and homeostasis in developing organisms. Presumably, this occurs when the hormone induces a qualitative change in the pattern of gene expression. Thus, identifying and characterizing the gene targets for steroid action, and how they are translated into biological changes in the target tissue, is a primary goal of this research. Specifically, this proposal is a logical extension of the unexpected discovery made during the PI's post-doctoral studies on tissue-specific (salivary gland) steroid-regulated genes in the fruit fly Drosophila melanogaster. Briefly, it was shown that E63-1, a primary (early) target for the Drosophila steroid ecdysone, encodes a high-affinity Ca2+-binding protein. This discovery was novel and exciting because most of the previously characterized early targets were shown to encode transcription factors. This finding provides the first link between steroid-regulated and Ca2+-regulated signaling pathways in Drosophila. Thus, one is afforded a unique opportunity to investigate this possible "crosstalk" in a genetically tractable organism in the context of an already well characterized molecular hierarchy. The overall hypothesis being addressed is that E63-1 functions to coordinate a steroid- and calcium-mediated regulatory pathway in the salivary gland. The goals are to dissect this pathway at the molecular level, investigate the possibility that E64-1 encodes a signal transduction molecule, and apply this information to other systems. The specific aims are as follows: 1) Genetically manipulate the levels of E63-1 protein and investigate these effects on the physiological state of the tissue (secretory activity, gene expression manifested as puffs, intracellular Ca2+ changes). 2) Further define the mechanism by initiating a molecular screen for downstream acceptor proteins of E63-1.